India's prime minister, Manmohan Singh, has called for a collective effort to protect women in the country as protests continued in Delhi after the rape of a five-year old girl last week.

The victim, left for dead after being imprisoned and starved for two days in an apartment in the Indian capital, was said to be improving by doctors. The girl had sustained serious internal injuries during a series of assaults.

Police were heavily criticised after the December incident and have also been the focus of protesters' anger this time.

In the latest case, officers allegedly initially refused to investigate after the girl, from a working class family, disappeared while playing early in the evening outside her home. She was eventually found by neighbours. When the case was picked up by the local media, the parents were offered 2,000 rupees (£25) to drop the case, relatives of the victim have said. A labourer who had been staying nearby has been arrested for attack.

Manmohan Singh has called for an end to the depravity. Photograph: AFP Prakash Singh/AFP

"The gruesome assault on a little child a few days back reminds us of the need to work collectively to root out this sort of depravity from our society," the prime minister said.

A series of laws have been passed stiffening penalties for sexual assault and making sexual harassment a crime. However "eve-teasing" – as the physical or verbal molestation of women in public places is euphemistically known – is endemic.

"Our government has moved with speed in strengthening the law to be able to deal more effectively with offences against women," Singh told an audience of civil servants on Sunday. "The safety, security and status of women in our country is a matter of concern. We have to make vast improvements in this area."

India's political leaders have struggled to respond to public anger over the continuing attacks on women and Singh's speech is unlikely to allay criticism that his government has not done enough to protect women.

The incident damaged the country's image, causing a drop in tourism, a major employer and significant foreign exchange earner.

Protesters from the Bharatiya Janata party, the main opposition, clashed with police outside the official residence of Sonia gandhi, president of the ruling Congress party.

A senior police officer has been suspended after images of him slapping a protester were broadcast.

International campaign groups today called for reforms.

"This case shows the appalling extent of indifference in the police to violence against women and girls, and the inadequacy of internal processes to ensure professional conduct" said G Ananthapadmanabhan, chief executive of Amnesty International India.

There have been a spate of incidents involving sexual violence to minors in recent days. In the past 36 hours, there have been reports of rapes of a four-year-old girl by a 14-year-old neighbour in Fatehabad district in the northern state of Haryana, a five-year-old girl in Ghansour town near Seoni in central Madhya Pradesh, and a six-year-old girl was raped in a village in Uttar Pradesh's Bulandshahr. Two rapes of 12 year olds were also reported. Another incident in Delhi involved a 13-year-old who attempted to kill herself after being assaulted by eight men and abused over a nine-day period last month.

In a further incident last week, a woman was repeatedly raped in a moving car by men who gave her a lift in the south of the city after she found herself locked out of a relative's home.